Light-emitting diodes (i.e. LEDs) are used as light sources for various light-emitting instruments such as lighting appliances, traffic signals, backlights for liquid crystal displays, etc. The light-emitting diodes, in particular, high intensity light-emitting diodes, are more generally used because they have longer lifetimes and lower power consumption compared to the whitish color lighting units such as incandescent light bulbs, halogen lamps, mercury lamps, fluorescent lamps, etc.
As shown in FIG. 12, the LED that is used as a light source of a conventional light-emitting instrument has a light-emitting component 33 which is mounted on a substrate 40 made of alumina ceramics, glass fiber-containing epoxy resins or bismaleimide-triazine resins. And leads 34a, 34b that extend from the light-emitting component 33 are connected to a wiring 35a, 35b on the substrate 40 respectively. The light-emitting component 33 on the substrate 40 is surrounded by a small whitish color package molding member (i.e. reflector) 30 measuring approximately several millimeters to several centimeters. The whitish color package molding member is made of resin such as polyether, polyphthalamide, polyether ether ketone or precious ceramics such as alumina, and has an opening in a light exiting direction. These devices and members mentioned above are integrated into one body to constitute a semiconductor light-emitting unit.
In a case where the substrate 40 or the package molding member (i.e. reflector) 30 is made of the resin, the resin is thermally degraded during lead-free-reflow soldering by which the semiconductor light-emitting unit is fixed to a circuit, and is photo-degraded when the wavelength is in an ultraviolet region. In particular, in a case where high intensity light-emitting diodes are used, the light gradually causes inferiority through yellowing or browning, dullness in the surface color and deterioration in light reflectance of the resin, due to high intensity of the strong emitted light and high temperatures associated with it. On the other hand, in a case where the substrate 40 or the package molding member (i.e. reflector) 30 are made of ceramics, no photo and thermal degradations due to ultraviolet ray are observed, but the emitted light tends to leak out, obtaining insufficient illuminance.
The surface of the substrate or the package molding member has been plated so as to reflect light. When the surface is plated with silver, high reflectance of light is obtained but the reflectance is deteriorated when sulfurization occurs to be blackish, being unfavorable. When the surface is plated with gold, excellent anti-sulfurization and anti-oxidation properties are achieved, but the reflectance becomes low, cost rises and it lacks versatility, too, being unfavorable. Furthermore, high precision plating treatments are required for the surface of these small substrates and the package molding members, so that complex steps are needed in plating process, accordingly productivity also decreases, being unfavorable, too.
In Japanese Patent Publication JP2006-343445A, a light reflecting material is disclosed. It is prepared without plating processes, has resistant to light deterioration and is less likely to leak light. The light reflecting material has a weather resistant layer with an ultraviolet ray absorbing function on one surface of a light reflecting layer, and also has a light shielding layer on the other surface. The light reflecting layer comprises a composition including an aromatic polycarbonate resin and a rutile-type titanium oxide of white pigment with low catalyzing activity for decomposition.
Light-emitting diodes that are capable of emitting light having a short wavelength region near lower limit of the visible region or the ultraviolet region have been manufactured recently. A reflecting material made of plastics such as a rutile-type titanium oxide-containing polycarbonate resin cannot sufficiently reflect light that is emitted from such light-emitting diode and has a wavelength region of 360 nm or over near the lower limit in the visible region, in particular, the wavelength region of 380 to 400 nm.
In Japanese Patent Publication JP2008-143981A, a semiconductor light-emitting unit is disclosed, in which a base plate and a light-emitting component are bonded with a resin composition. The resin composition comprises an anatase-type titanium oxide that is dispersed in an epoxy resin, and has a good light reflecting efficiency in a broad wavelength region. However, change in light reflectance with time is large, and the epoxy resin is gradually degraded. Therefore, the light reflecting efficiency deteriorates with time.
Furthermore, in light-emitting diodes, silicone type sealing resins which have excellent heat-resistance and light-resistance have come into use as sealing resins under a trend of shortening in wavelength and increasing in output power of emitting light. However, their adhesiveness is insufficient due to differences in, for example, a degree of shrinkage between the silicone type sealing resin and the conventional package member made of resin such as polyether, polyphthalamide, polyether ether ketone, etc. Accordingly, newly designed packages are desired.
The conventional reflecting material made of plastics cannot efficiently reflect light of the wavelength region of 380 to 400 nm and a longer wavelength region in the visible region and a heat ray having further longer wavelength in the infrared region as heat rays. Therefore, a general-use reflecting material is desired, which can sufficiently reflect such wavelength light, can exhibit excellent heat and light resistances, and has no change in color, excellent durability and no declining in light reflectance after a long period of use. It can also be used not only for lighting equipment that emits light but also for a solar cell assembly that converts sunlight into electricity.